The subject matter of this application relates to reflex printing, and more specifically provides a device and method for reducing printing defects resulting from a phase difference in an encoder error function, such as stitch error correction.
In reflex printing, a cylindrical drum rotates past a print head which ejects ink onto the surface of the drum. In traditional reflex printing devices, there is only one print head. Therefore, the entire image is ejected by one full-width print head. The print head is made-up of an array of very small orifices through which liquid ink is ejected. The print head is fired according to a drum position signal, rather than a time-based synchronization signal.
The ink is ejected from the print head onto the drum and is built-up over a series of passes to form a complete image. Because a sufficient amount of ink cannot be deposited in one revolution of the drum to create the entire image, a portion of the image is ejected per revolution of the drum. For example, a first portion of the image is ejected onto the drum in the first revolution. The print head is then shifted, or indexed left to right, i.e., along the axis of the drum and another portion of the image is ejected onto the drum. The process is repeated by indexing the print head along the axis of the drum until the complete image is built-up.
It is known to monitor the position of the imaging surface of the drum by a rotary motion encoder and to control the output of data by a print head or an image bar which forms a latent image on the imaging surface so that an image, such as characters, are formed at the proper locations on the imaging surface. In practice, the encoder may be mounted slightly off of the axis of drum rotation leading to a “runout”-type error in the encoder reading. Such “runout” results in stitching errors in the process direction. That is, the output in the process direction from one print head is not aligned relative to the output in the process direction of a second print head.